Methods for transmission time interval bundling in the uplink

ABSTRACT

Methods, systems, and apparatus for supporting uplink Transmission Time Interval (TTI) bundling in Long Term Evolution (LTE) are provided. Methods, systems, and apparatus for signaling, activation/deactivation, and wireless transmit/receive unit (WTRU) behavior are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/851,257, filed Sep. 11, 2015, which will issue as U.S. Pat. No.10,104,655 on Oct. 16, 2018, which is a continuation of U.S. patentapplication Ser. No. 12/421,838, filed Apr. 10, 2009, which issued asU.S. Pat. No. 9,172,509 on Oct. 27, 2015, which claims the benefit ofU.S. Provisional Application No. 61/044,111, filed Apr. 11, 2008;61/052,725, filed May 13, 2008; 61/083,789, filed Jul. 25, 2008; and61/081,444, filed Jul. 17, 2008, the entire contents of all of which areincorporated herein by reference.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

Third generation partnership project (3GPP) and 3GPP2 are consideringlong term evolution (LTE) for radio interface and network architecture.There is an ever-increasing demand on wireless operators to providebetter quality voice and high-speed data services. As a result, wirelesscommunication systems that enable higher data rates and highercapacities are a pressing need.

In evolved Universal Mobile Telecommunication System (UMTS) TerrestrialRadio Access (evolved UTRA), the network architecture includes a radioaccess network that provides wireless transmit/receive units (WTRUs)access to a core network of a cellular communication system. Within theradio access network, radio resources are divided into blocks of time(sub-frames) and frequency (frequency blocks).

Transmission Time Interval (TTI) bundling in the uplink has beenproposed to improve coverage for WTRUs near the cell edge. The solutionis characterized by a single transport block that is coded andtransmitted in a set of consecutive subframes. A bundle is treated as asingle resource, i.e., a single grant, and a single hybrid-AutomaticRepeat Request (HARQ) acknowledgement is used for each bundle. The sameHARQ process number is used in each of the bundled subframes. The HARQRound Trip Time (RTT) is different than for the non-bundling case toreduce delays. The relation between subframe number and HARQ processnumber is unaffected for non-bundled subframes. Bundling can be appliedto Frequency Division Duplex (FDD) as well as Time Division Duplex(TDD). For TDD, the bundling size needs to take the allocations ofsubframes to Uplink (UL) and Downlink (DL) into account.

For an example in a LTE FDD system, a HARQ process and its differentredundancy versions (RV) are bundled and transmitted in a fixed numberof subframes, timeslots or applicable blocks of time or frequency andmay be designated as N_(bundle) and may also referred to as the TTIbundling value. For example, N_(bundle)=4, is the current workingassumption in 3GPP standards. A single transport block may be coded andtransmitted in a set of consecutive subframes.

Three alternatives for TTI bundles are shown in FIG. 1, FIG. 2 and FIG.3, respectively. In Alternative 1, the timing relation between the lastsubframe in the TTI bundle and the transmission instant of the HARQacknowledgement is identical to the case of no bundling. For the case ofFDD, if the last subframe in a TTI bundle is subframe n, then theacknowledgement is transmitted in subframe n+4 and if the first subframein a TTI bundle is subframe k, then any HARQ retransmissions begins insubframe k+2*HARQ_RTT. In Alternative 2, the timing relation between thefirst subframe in the TTI bundle and the transmission instant of theHARQ acknowledgement is identical to the case of no bundling. For thecase of FDD, the HARQ acknowledgement is obtained from decoding thefirst subframe only. In Alternative 3, the timing relation between thelast subframe in the TTI bundle and the transmission instant of the HARQacknowledgement is identical to the case of no bundling. For the case ofFDD, if the last subframe in a TTI bundle is subframe n then theacknowledgement is transmitted in subframe n+4

Uplink TTI bundling may be activated and deactivated by radio resourcecontroller (RRC) signaling. When switched on, TTI bundling applies toall uplink transmissions using PUSCH. To reduce the number of optionsand the associated testing, the number of configurations of the bundlesize is minimized. Preferably only a single fixed value of the number ofsubframes in a bundle is specified. But there are several deficiencieswith respect to this method such as but not limited to not providingcriteria for triggering TTI bundling, no defined WRTU behaviors, no HARQprocess related behaviors and no details related to Semi-PersistentScheduling (SPS).

SUMMARY

The present application discloses methods and apparatus for supportingTTI bundling in the uplink in evolved Universal Mobile TelecommunicationSystem (UMTS) Terrestrial Radio Access (evolved UTRA) that includes forexample new signaling mechanisms including the use of Physical DownlinkControl Channel (PDCCH) and Medium Access Control (MAC) Control Element(CE) signaling, triggering criteria, activation and de-activationmethods, wireless transmit/receive units (WTRU) behavior definitions,and TTI bundling with Semi-Persistent Scheduling.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows a Transmission Time Interval (TTI) bundling sequence;

FIG. 2 shows an alternate TTI bundling sequence;

FIG. 3 shows another alternate TTI bundling sequence;

FIG. 4 shows an example functional block diagram of a wirelesstransmit/receive unit (WRTU) and a base station;

FIG. 5(a) shows a standard Physical Downlink Control Channel (PDCCH)Downlink Control Information (DCI) format 0;

FIG. 5(b) shows a PDCCH DCI format 0 in accordance with an exampleembodiment;

FIG. 6(a) shows a PDCCH DCI format 0 in accordance with another exampleembodiment;

FIG. 6(b) shows a PDCCH DCI format 0 in accordance with yet anotherexample embodiment;

FIG. 7 shows an example Information Element Medium Access Control (MAC)Configuration table in accordance with an example embodiment;

FIG. 8 shows an example TTI bundling diagram in accordance with anexample embodiment;

FIG. 9 shows another exemplary TTI bundling diagram in accordance withan exemplary embodiment;

FIG. 10 shows an example hybrid-automatic repeat request (HARQ) processtransmission after a TTI bundling deactivation in accordance with anexample embodiment;

FIG. 11 shows an example TTI bundling diagram with an uplink grant inaccordance with an example embodiment; and

FIG. 12 shows an example Information Element MAC Configuration table forSemi-Persistent Scheduling in accordance with an example embodiment.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

Referring now to FIG. 4, there is shown an example functional blockdiagram 100 of a WTRU 110 and a base station 150 in communication withone another and may be configured to activate, deactivate, processand/or otherwise support Transmission Time Interval (TTI) bundling.

In addition to the components that may be found in a typical WTRU, theWTRU 110 includes a processor 115, a transmitter 120, a receiver 125,and at least one antenna 130 to facilitate wireless communication. Theprocessor 115 is configured to perform a method for activating,deactivating, processing and/or otherwise supporting TTI bundling in awireless communication system in accordance with the presentapplication. The receiver 125 and the transmitter 120 are incommunication with the processor 115. The antenna 130 is incommunication with both the receiver 125 and the transmitter 120 tofacilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical basestation, the base station 150 includes a processor 155, a receiver 160,a transmitter 165, and at least one antenna 170. The processor 155 isconfigured to perform a method for activating, deactivating, processingand/or otherwise supporting TTI bundling in a wireless communicationsystem in accordance with the present application. The receiver 160 andthe transmitter 165 are in communication with the processor 155. Theantenna 170 is in communication with both the receiver 160 and thetransmitter 165 to facilitate the transmission and reception of wirelessdata.

The following discussion presents signaling methods for TTI bundling,triggering criteria to activate/deactivate TTI bundling, activation anddeactivation details, WRTU behavior upon activation and deactivation,processing issues, partial services with respect to TTI bundling and theuse of Semi-Persistent Scheduling (SPS) with TTI bundling.

Signaling Methods And Information Provided

In addition to signaling using Radio Resource Control (RRC), exemplarymethods for signaling and/or supporting TTI bundling include using thePhysical Downlink Control Channel (PDCCH) and the Medium Access Control(MAC) Control Element (CE).

In an exemplary embodiment, PDCCH signaling is used as a method ofsignaling that supports TTI bundling. The PDCCH is used to carrydownlink control information (DCI) such as scheduling grants,assignments, power-control commands, uplink scheduling grants, resourceblock allocations/assignments, and HARQ related information. The PDCCHcarries multiple DCI formats depending on the type of required controlinformation.

FIG. 5(a) and FIG. 5(b), show a DCI format 0 for a standard uplink grantand a DCI format 0 for an uplink grant that supports TTI bundling. TheDCI format 0 includes multiple fields but for the purposes of thepresent description the relevant fields are Resource Block (RB)Allocation/Assignment; Modulation and Coding Scheme (MCS); andDemodulation Reference Symbol (DMRS).

Referring specifically to FIG. 5(b), the PDCCH can use one reserved orspare bit-field in either the RB allocation field, the MCS field or theDMRS field of the existing PDCCH DCI format 0 to indicateactivation/de-activation of TTI bundling for the WRTU. In anillustrative embodiment, in PDCCH DCI format 0, a RB allocation fieldwith “0000000000000” can be used to activate TTI bundling. The remainingfields of the disclosed PDCCH DCI format 0 can be used to indicate theTTI bundling configuration and necessary information for PUSCHtransmission. The TTI bundling configuration information can include,but is not limited to activation/deactivation of TTI bundling for theWRTU; the number of bundled subframes (when and if applicable); and themaximum number of hybrid-automatic repeat request (HARQ)re-transmissions. Other TTI bundling configuration information can beprovided as necessary such as, for example, the redundancy version (RV)value as further explained below.

A limited RB allocation and MCS may be used for the Physical UplinkShared CHannel (PUSCH) when TTI bundling is applied, since the radiolink condition may be very weak. The MCS and/or DMRS fields can be usedto signal restricted RB allocation, MCS, the number of bundled TTIs orsubframes and the TTI bundling configuration.

Referring now to FIG. 6(a) and FIG. 6(b), another example embodiment isshown using PDCCH signaling. In this example embodiment, the method usesPDCCH DCI formats 0 and 1A that are aligned (e.g., the same length) asshown in FIGS. 6(a) and 6(b), respectively. In this example embodiment,the PDCCH DCI format 0 adds an additional bit that provides the paddingin order to have the same length as PDCCH DCI format 1A and theadditional bit of DCI format 0 may be used to support TTI bundlingswitching and/or activation. When the TTI bundling bit is set to 1, itis an indication that TTI bundling is activated. The remainder of thePDCCH DCI format 0 can be used to indicate the rest of the TTI bundlingconfiguration and information necessary for PUSCH transmission. Aspreviously stated above, limited/restricted RB allocation and MCS may beused for PUSCH when TTI bundling is applied since the radio linkcondition may be very weak. The RB allocation, MCS and/or DMRS fieldscan be used to signal restricted RB allocation, MCS, the number ofbundled TTIs or subframes and the TTI bundling configuration.

In another embodiment, a medium access control (MAC) control element(CE) is used to provide signaling for TTI bundling in the uplink. Thiscan be a special MAC_CE used for TTI bundling signaling, e.g.,activation/deactivation, along with providing the TTI bundling value orcan be combined with other parameters in one MAC_CE. The TTI bundlingvalue refers to the number of subframes, timeslots or other applicableunits that are bundled together and treated as one unit. The MAC_CEheader can indicate that this MAC_CE is TTI bundling signaling in theuplink. The contents of the MAC_CE can be the same as that proposed forusing PDCCH signaling. Radio Resource Control (RRC) decides whether touse MAC_CE or PDCCH for TTI bundling signaling.

The MAC_CE can be used both for the configuration and reconfiguration ofa TTI bundling value to the WTRU. The MAC_CE, to configure a TTIbundling value, can be sent at the time when a new service and/orconnection is established or can be sent after the service and/orconnection is established to reconfigure the TTI bundling parametersincluding a TTI bundling value. The MAC_CE includes a TTI_Bundle_Valuewhich can be set to 2, 4, 8 in this example, although other integervalues could also be used in alternate embodiments.

As stated above, the RV value may to be provided in the signalingmessage. The RV value used for TTI bundling can be the same or differentthan the TTI bundling value. The RV values should correspond to thedifferent number of TTIs that are to be used for the TTI bundle, e.g.,RV values for 2, 4 or 8 bundled TTIs (as is currently proposed). It maybe configured dynamically or semi-statically. When RV values used forTTI bundling are semi-static, they can be signaled during theconfiguration or re-configuration phase through RRC or MAC_CE signaling.If RV values for TTI bundling are dynamic, then they can be signaledduring TTI bundling activation through MAC_CE or PDCCH signaling.

When RRC message signaling is used to signal RV values, these values arecontained in the IE MAC-Configuration (MAC-Configuration informationelement (IE)) which is used to specify the MAC layer configuration fordata radio bearers as shown in FIG. 7. In an example embodiment, the RRCcan signal all the RV values for all of the different TTI bundlingvalues or in another embodiment, the RRC can signal RV valuescorresponding to the configured TTI bundling value. In the semi-staticexample embodiment, RVs for the configured TTI bundling value should besignaled.

In an example embodiment for when MAC_CE signaling is used for RVvalues, the MAC_CE can signal all the RV values for all of the differentTTI bundling values or in another embodiment, the MA_CE can signal RVvalues corresponding to the configured TTI bundling value. In thesemi-static exemplary embodiment, RV values for the configured TTIbundling value should be signaled.

Criteria To Trigger (Activate) TTI bundling

The criteria to trigger TTI bundling can be based on any combination ofthe following factors: Pathloss—this factor can indicate whether theWTRU is at the cell edge and if the WTRU is at cell edge this may meanthe uplink channel quality is low; Signal to Noise and Interferenceratio, e.g., SINR—this factor can indicate the signal quality and theinterference level; number of retransmissions or number of NAKs,etc.—this factor can directly reflect the transmission quality; Qualityof UL sounding channel—this factor can indicate whether the uplinkchannel has good quality; Quality of Service (QoS)—this indicator canreflect the priority and delay requirement of the service; powerheadroom; and uplink channel capacity. Analysis of the above factors canbe used to determine whether to trigger TTI bundling in the followingretransmissions.

Activation Details

Activation of TTI bundling can be included in the PDCCH when making theresource allocation for retransmission by the base station, e.g., anevolved NodeB (eNB). Activation can also or alternatively beaccomplished using a MAC_CE. The activation can be signaled to a WTRUexplicitly or implicitly.

Explicit activation of TTI bundling can occur by using a one bitindication contained in the uplink grant of the PDCCH; a one bitindication at any other pre-defined position in the PDCCH; or by using aMAC_CE, where the MAC_CE can contain an indication to activate TTIbundling.

Implicit activation of TTI bundling can occur if the uplink grantindicates that the resource allocation for retransmission of theinitially transmitted packet is across several TTIs rather than one TTI.After the WTRU detects this information, the WTRU knows that thisimplies that the TTI bundling should be used in the followingretransmissions. When semi-static TTI bundling is used, the WTRUimplicitly knows from the RRC or MAC_CE because of the TTI bundlingvalue that is sent for the retransmissions.

There are two scenarios for uplink resource allocation forretransmissions using TTI bundling, thus different signaling methodsshould be used in PDCCH:

Scenario 1: The same physical resources, (such as frequency bands andantenna, etc), transport format (such as MCS and power, etc), HARQparameters (such as RV values) will be used for different TTIs in thesame TTI bundle. In this scenario the uplink grant contained in PDCCHonly needs to signal resource allocation parameters for one TTI. Theactivation of TTI bundling will automatically imply to use the sameresource allocation for the other TTIs (or subframes) in the TTI bundle.

Scenario 2: Different physical resources, transport format and HARQparameters will be used for different TTIs in the TTI bundle. Also thesame RV values or different RV values can be applied to different TTIsin the TTI bundle. In this scenario the uplink grant contained in thePDCCH signals resource allocation parameters for all different TTIs inthe TTI bundle. This can also implicitly indicate to the WTRU that TTIbundling is used for retransmissions.

De-activation Details And WTRU Behavior

De-activation of uplink TTI bundling and the corresponding WTRU behavioris now described. In an example embodiment, whenever the WTRU receivesan ACK from a previous retransmission using TTI bundling, then the WTRUknows that the retransmission using TTI bundling has been successful andno more TTI bundling will be used for this packet. The WTRU should clearthe HARQ buffer related to that HARQ process.

When uplink TTI bundling is activated when at least one HARQ process isstill active, (e.g., the WTRU is waiting for HARQ feedback or has apending retransmission), the following provides example WTRU behaviors.

In an example embodiment, the WTRU keeps the currently active HARQprocess running until either a successful transmission occurs or themaximum number of retransmissions is reached. After that, TTI bundlingis activated at the WTRU. From the time the RRC message is received tothe time TTI bundling becomes effective at the WTRU's side, the basestation, e.g., an eNB, should not schedule any uplink new datatransmissions where the starting time falls in that range.

In another example embodiment, the WTRU applies TTI bundlingimmediately. The TTI bundle size N_(bundle) determines the maximumnumber of HARQ processes, N_(HARQ) _(_) _(bundle) _(_) _(max), when TTIbundling is used. For example, for N_(bundle)=4, N_(HARQ) _(_) _(bundle)_(_) _(max) equals to 4. If the number of currently active HARQprocesses at the WTRU is more than N_(HARQ) _(_) _(bundle) _(_) _(max),it needs to be reduced to at most N_(HARQ) _(_) _(bundle) _(_) _(max). Apre-defined rule for which HARQ processes to keep or flush should beknown to both the WTRU and the base station.

In another example embodiment, the base station does not schedule anynew data transmission for the WTRU for a fixed duration, say T. Theduration Tis long enough so that currently active HARQ processes at theWTRU will either succeed or fail after the maximum number ofretransmissions when T expires. Then (after the duration of T), the basestation will send signaling to the WTRU to activate uplink TTI bundling.

When uplink TTI bundling is deactivated when at least one HARQ processis still active, (e.g., it waits for HARQ feedback or has a pendingretransmission), the following provides example WTRU behaviors.

In an example embodiment, the WTRU keeps the currently active HARQprocess running until success or failure occurs after the maximum numberof retransmissions is reached. After that, TTI bundling becomes disabledat the WTRU's side. From the time the RRC message is received to thetime TTI bundling becomes disabled at the WTRU's side, the base stationshould not schedule any uplink new data transmission whose starting timefalls in that range.

In another example embodiment, the WTRU applies TTI bundlingimmediately. Within one bundle-mode HARQ round-trip-time (RTT), thereare at most N_(HARQ) _(_) _(bundle) _(_) _(max) active HARQ processes atthe WTRU. There are several example cases.

In example case 1, if the time that TTI bundling deactivation signalingis received at the WTRU is early enough to allow the WTRU to stoptransmission for the next bundled HARQ process, then the WTRU transmitsthe next (and subsequent) HARQ process in the non-bundled mode insteadof bundle-mode, as shown in FIG. 8.

In example case 2, if the time that TTI bundling deactivation signalingis received at the WTRU is not early enough to stop transmission for thenext bundled HARQ process, say process n, then as shown in the exemplaryexample in FIG. 9, the WTRU should 1) transmit the HARQ process n in thebundled mode and 2) transmit the HARQ process n+1 (and subsequent ones)in the non-bundled mode instead of bundle-mode.

In another example embodiment, the base station does not schedule anynew data transmission for the WTRU for a fixed duration, say T. Theduration Tis long enough so that currently active HARQ processes at theWTRU will either succeed or fail after the maximum number ofretransmissions when T expires. Then (after the duration of T), the basestation sends signaling to the WTRU to deactivate uplink TTI bundling.

When the WTRU switches from bundle mode to non-bundle mode (afterreceiving deactivation signaling), existing active HARQ processes inbundle-mode may need to be converted to non-bundle mode. Accordingly,HARQ processes converted from bundle-mode HARQ processes may betransmitted in the order of bundle-mode HARQ processes, as shown in FIG.10.

Synchronization Processing

If uplink TTI bundling activation/deactivation is not properlyconfigured or synchronized between the WTRU and base station, theproblem needs to detected and corrected. The following example methodsfor detection of the problem may be employed.

In an example embodiment, the WTRU detects the(de)activation/synchronization problem. If the WTRU thinks it isconfigured for TTI bundling but receives an uplink grant conflictingwith the current TTI bundling, it may regard the TTI bundling as notbeing configured correctly or the TTI bundling is not synchronizedbetween the WTRU and base station. For example, the WTRU receives anuplink grant which schedules a new data transmission that will conflictwith its TTI-bundled transmission, as shown in FIG. 11.

In another example embodiment, the base station detects theactivation/synchronization problem. For a WTRU that has been configuredin the bundle-mode by the base station, if the base station detects thatin the same bundle, one or several of the 2^(nd), 3^(rd), 4^(th) HARQtransmissions has an energy level below a pre-determined threshold, thenit will consider it as that WTRU is not (properly) configured inbundling mode.

For a WTRU that has been configured in the non-bundle mode by the basestation, if the WTRU is not scheduled to transmit in subsequent 2^(nd),3^(rd), 4^(th) sub-frames following an uplink data transmission in a setof RBs denoted by S, but the base station detects 1) energy levels atthe set S (or a subset of S) in subsequent 2^(nd), 3^(rd), 4^(th)sub-frames is above a (pre-determined) threshold even when set S (or asubset of S) is not allocated to other WTRUs; or 2) a collision withother WTRUs scheduled transmission on the set S (or a subset of S) insubsequent 2^(nd), 3^(rd), 4^(th) sub-frames; then upon detecting theTTI bundling (de)activation/synchronization problem, the base stationactivates/deactivates the WTRU for uplink TTI bundling again.

Partial Services

In an example embodiment, when TTI bundling is configured for a WTRU, itis configured for all of its services. In another example embodiment, apartial (or mixed) TTI bundling mode can be configured. For illustrativepurposes, a WTRU can be configured to use TTI bundling for low latencyservices, such as for example, voice or services with small radio linkcontrol (RLC) packet data unit (PDU) sizes. On the other hand, a WTRUcan transmit in non-bundle mode for best effort services or serviceswith large RLC PDU sizes.

TTI Bundling And Semi-Persistent Scheduling.

In an example embodiment, whether TTI bundling is used inSemi-Persistent Scheduling (SPS) mode may be predefined in the 3GPPstandard or configured in a RRC or MAC_CE message signaling during theconfiguration phase, the reconfiguration phase, or both. When TTIbundling is used for SPS, the radio resource for retransmission may notbe signaled by the base station via the PDCCH. However, this operationneeds to be signaled by the base station so that the WTRU knows toperform retransmissions during SPS without waiting for reconfigurationsignaling from the base station The RRC or MAC_CE may signal to the WTRUwhether the radio resource for retransmission will be reconfigured ifTTI bundling is used for SPS.

If no reconfiguration is indicated, then predefined frequency andresource blocks may be used for TTI bundling. The predefined radioresources may be the same for all bundled subframes, or the radioresources may vary from subframe to subframe according to the RRC orMAC_CE configuration. The variation may be a certain hopping pattern inthe frequency domain. If it receives a NAK, the WTRU may not use thepredefined radio resources for other uplink transmissions.

When there is no need for reconfiguration for TTI bundling for SPS, theredundancy version (RV) value used for TTI bundling may be the same asis used for the initial transmission.

When there is no signaling for retransmission resource allocation, andan uplink TTI-bundled retransmission collides with a subsequent initialTTI-bundled transmission, the initial transmission should take thehigher priority. This means that, either the retransmission should becanceled or resource allocation is needed.

When a RRC message is used to signal whether to use TTI bundling for SPSand whether to allow reconfiguration of resource for retransmissions, itcan be contained in the Information Element (IE) MAC-Configuration,which is used to specify the MAC layer configuration for data radiobearers as shown in FIG. 12.

When TTI bundling is used for SPS and the base station signals resourceallocation for retransmissions, the PDCCH may only contain the resourceallocation information for the first subframe. The WTRU may use the sameresource allocation for other subframes in the same bundle.

If the frequency and resource blocks are different subframe by subframe,then the resource allocation for retransmissions can be signaled for allthe subframes used for TTI bundling.

Activation and De-activation TTI Bundling for SPS via layer oneSignaling, layer two Signaling, or both.

Activation of UL TTI Bundling

In an example embodiment, activation of uplink TTI bundling for SPS maybe included in the PDCCH when making the resource allocation forretransmission by the base station. In another embodiment, activationcan be done by using the MAC CE. The activation can be signaled to theWTRU explicitly or implicitly. Signaling for both methods is consideredas follows.

Explicit activation of TTI bundling can occur by using a one bitindication in the uplink scheduling grant carried on the PDCCH; a onebit, or one code-point, indication at any other pre-defined position inthe uplink scheduling grant carried on the PDCCH; or by using theMAC_CE, where the MAC_CE can contain an indication to activate TTIbundling for SPS.

Implicit activation of TTI bundling can occur if the uplink grantindicates that the resource allocation for retransmission of theinitially transmitted packet is across several TTIs rather than one TTI.After the WTRU detects this information, the WTRU knows that thisimplies that TTI bundling should be used in the followingretransmissions. When semi-static TTI bundling is used, the WTRUimplicitly knows from the RRC or MAC_CE because of the TTI bundlingvalue that is sent for the retransmissions.

There are two scenarios for UL resource allocation for retransmissionsusing TTI bundling for SPS, thus different signaling methods should beused in PDCCH.

Scenario 1: The same physical resources (such as frequency bands andantenna, etc.), transport format (such as MCS and power, etc.), HARQparameters (such as RV values), may be used for different TTIs in thesame TTI bundle. In this scenario, the uplink grant contained in thePDCCH may signal resource allocation parameters for the first subframe.The activation of TTI bundling will automatically imply the use of thesame resource allocation for the rest of the TTIs in the TTI bundle.

Scenario 2: Different physical resources, transport formats and HARQparameters may be used for different TTIs in the TTI bundle. Either thesame RV values or different RV values can be applied to different TTIsin the TTI bundle. In this scenario, the uplink grant contained in PDCCHmay signal resource allocation parameters for all different TTIs in theTTI bundle for SPS retransmission. This may implicitly indicate to theWTRU that TTI bundling is used for retransmissions.

De-activation of Uplink TTI Bundling and WTRU Behavior

De-activation of uplink TTI bundling and the corresponding WTRU behaviormay be such that when the WTRU receives an ACK for a previousretransmission using TTI bundling, the WTRU knows that the transmissionusing TTI bundling is successful and no more TTI bundling will be usedfor the packet. The WTRU should clear the HARQ buffer related to thatHARQ process.

A method and apparatus for supporting uplink TTI bundling in LTE isprovided. Described above are related method and apparatus forsignaling, activation/deactivation and WTRU behavior. Signaling andwireless transmit receive unit behavior for transmission time intervalbundling with semi-persistent scheduling in long term evolution isdisclosed. Methods to support uplink TTI bundling in Semi-PersistentScheduling (SPS) may include the use of RRC or MAC_CE. These signals maybe used to inform the WTRU that the radio resources for retransmissionwill be reconfigured. Predefined frequency and resource blocks may beused for TTI bundling. The message can be contained in the InformationElement (IE) MAC Configuration. Both activation and deactivation of TTIbundling are supported, and may be indicated explicitly or implicitly.Different signaling schemes may be used depending on whether the samephysical resources are used for retransmissions.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU), the WTRUcomprising: a memory, and; a processor, the processor being configuredto: receive, via a physical downlink control channel (PDCCH), atransmission time interval (TTI) bundling message that enables the WTRUto support uplink TTI bundling, the TTI bundling message including a TTIbundling active/de-activate field and a TTI bundling configuration;determine a hybrid acknowledgement repeat request (HARQ) process state;determine an TTI bundling procedure using the TTI bundling message andthe HARQ process state; and send a transmission via a physical uplinkshared channel (PUSCH) using the TTI bundling procedure.